Auto-classify a selection

I posted this over on formscoding, but didn't get a response. I'm reposting
here in hopes maybe this is the right forum. Thanks.

Access 2003, XP Srvc Pack 3

I want to automatically classify an entry based on its selection.

Details so far:

tblContact (contains standard info about the contact)
tblContactType (an ID# field and description [classifications for the
contact such as vendor, employee, etc.])
tblComboContactType (contains the ID# for each combination of contact and
type. Example fldComboContactID, fldContactTypeID, fldContactID)
tblMaster (contains info about each company)

Usually to populate the tblComboContactType I tie the main form to the
"Contact" table, the subform to the "ComboContactType" table, and use the
"ContactType" as the row source for a combo box. This works fine.

I want to create an entry form to capture which contacts can authorize
purchases on behalf of a given company.

What I'd like to do on the form is select the company (I know how to do this
part), present a combo box with entries for each contact associated with that
company (pretty sure I can do this), then have the combination of
contact/"fact that they can sign" (this is a unique contact type called
"signer") populate into my tblComboContactType (this is the part I don't know
how to do).

Any suggestions or pointers to figure out how to do this?

Thank you for your help.

Allison